1. Field of the Invention
This invention relates generally to wood cutting apparatus, and more particularly to an adjustable miter gage apparatus and method for making precision miter cut angles with conventional radial arm saws, table saws, band saws, router tables, and other woodworking machines by utilizing a flat base or table top having a large radius arc with adjustable gages located thereon which acts as a large protractor and allows the cutting angle to be accurately adjusted relative to the actual angle at which the saw blade is initially positioned by the machine.
2. Brief Description of the Prior Art
In general, low to moderately high cost radial arm and table saws are incapable of accommodating a precision miter adjustment. In the case of the radial arm saw, the mechanism that allows the radial arm to swing in an arc to cut a miter also prevents it from doing it well. The accuracy of the miter angle that can be set depends on the clearance, or free play in the swing arm mechanism and the ability of the operator to read a small and inaccurate miter degree scale. The swing arm mechanism must have some clearance and tolerances built in so that the arm can be raised and/or rotated. When the mechanism having free play is located very near the swing arm column, a very small clearance will allow the outer end of the radial arm to rotate through a relatively larger arc.
For example, if the swing mechanism is located 13/4" from the center of the column, a total clearance of 0.015" would allow the outer end of a 24" swing arm to move about 3/16" or rotate through 1/2.degree.. If the swing mechanism were located 24" away from the center of the column, the same 0.015" clearance would allow only 1/32.degree. rotation. If the operator were to attempt a 1/2.degree. correction, that 1/2.degree. correction could be completely absorbed in the free play of the swing mechanism. As a result, conventional radial arm saws are not reliable for making miter cuts, except for the most liberal requirements.
In the case of the table saw, the standard miter gage does not have the capability of fine adjustments and any adjustment will be compromised by any error in the 90.degree. prealignment of the miter gage to the miter gage slot.
The radial arm saw for sure, and the table saw to some extent have structures that can be dimensionally unstable that could compromise adjustments that are transferred through these structures. These compromised adjustments are probably ignored or not noticed for work that does not require close tolerance. For close tolerance work, these adjustments become unreliable.
A common practice to overcome these problems in the table saw is to use an adjustable drafting triangle to align the miter gage with the plane of the saw blade. However, the plane of the saw blade may not be parallel to the miter gage slot if the arbor is bent, the blade is warped, or if the arbor is not aligned 90.degree. from the miter slot.
A radial arm saw having a digital miter cut angle readout has recently been introduced commercially. The digital readout only shows angles in 1/2.degree. increments. Like most other radial saws, it has miter stops at 90.degree. and at 45.degree.. When the radial arm is moved to one of these stops, the stop pin will engage and the readout will show 90.degree. or 45.degree.. However, with the stop pin engaged and before applying the radial arm clamp, the radial arm can be moved through a small angle (about 1/4-3/8 of a degree) without a corresponding indication on the readout. Thus, the adjustment tolerance is not much better than .+-.1/2.degree. due to the inherent tolerances through the radial arm and column mechanisms.
There are several patents which disclose various saw attachments and apparatus.
Pease, U.S. Pat. No. 3,586,077 discloses an elongated plate-like bar having a longitudinal groove for use as a guide for portable power saws.
Stocker, U.S. Pat. No. 3,645,307 power saw guide having a base frame adapted to be clamped to a work table and includes an elongate guide rail adapted for adjustment about a vertical axis. A saw carriage is roller supported on the rail for longitudinal movements.
Dalton, U.S. Pat. No. 3,903,600 discloses a dove tail guide bar slidable within the base plate of an electric saw which includes an adjustable mitre gauge, a spring with a steel point for keeping the saw from vibrating off mark, and a clamp secured on the end of the guide bar securing the guide bar to the material being sawed. The device further includes and angle adjustment for angular saw cuts relative to a vertical axis.
Beekenkamp, U.S Pat. No. 4,062,390 discloses a pair of vice members mounted on a supporting structure which are disposed in side-by-side relation for clamping a track member therebetween. An elongated workpiece guide is pivotally mounted to the track member for angularly positioning the workpiece in the path defined by the track member and a sled slides in the track member and carries a portable saw or router.
Sheps et al, U.S. Pat. No. 4,335,512 discloses a pair of elongate relatively slidable guides for guiding a portable handheld power saw.
The present invention is distinguished over the prior art in general, and these patents in particular by an adjustable miter gage apparatus and method for making precision miter cut angles with conventional radial arm saws, table saws, band saws, router tables, and other woodworking machines having a miter gage by utilizing a flat base or table top having a large radius arc with adjustable gages located thereon which acts as a large protractor and allows the cutting angle to be accurately adjusted relative to the actual angle at which the saw blade is initially positioned by the machine. The present miter gage apparatus does not require angular pre-alignment between the miter gage apparatus and the woodworking machine and does not require the woodworking machine to be in correct pre-alignment.